Structural Characterization of Mixed (TiO2) x (ZrO2) y (SiO2)1- x - y Sol−Gels (0.05 ≤ x, y ≤ 0.15) by a Combination of X-ray and Spectroscopy Techniques

A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), Fourier transform infrared (FTIR), and 17O nuclear magnetic resonance (NMR) spectroscopies, small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD) has been used to study the atomic structure of (TiO2) x (ZrO2) y (SiO2)1- x - y xerogels (0.05 ≤ x, y ≤ 0.15). The samples were prepared by reacting Ti butoxide and Zr n-propoxide with acetylacetone, to reduce reactivity of the metal alkoxides, and then reacting with partially hydrolyzed tetraethyl orthosilicate. EXAFS and XANES results imply that simultaneous insertion of Zr and Ti oxides into a silica host network causes the metals to adopt environments similar to those observed for the corresponding binary Zr oxide− and Ti oxide−silica systems. XANES, SAXS, and XRD indicate that the samples with up to 20 mol % total metal loading remain homogeneous with heat treatment up to 500 °C. 17O NMR indicates that both Ti- and Zr-rich samples with 20 mol % total metal loading exhibit phase separation after heat treatment at 750 °C. After heat treatment at 1000 °C, the sample with x = 0.15 and y = 0.05 shows clear evidence from XRD of phase separation in the form of ZrTiO4 domains, which is not seen in other samples.